In Patent application Ser. No. 311,063 entitled "Recovery of Metal Values from Manganese Deep Sea Nodules", filed on Dec. 1, 1972, by Lester J. Szabo, the teachings of which are incorporated herein by reference, a process is disclosed in which copper, nickel, cobalt and molybdenum are recovered from raw manganese nodules with an aqueous ammoniacal leach solution containing cuprous ions. The process disclosed in application Ser. No. 311,063 is a significant breakthrough in the metallurgical art in that it significantly expands the world's source of copper, nickel, cobalt and molybdenum. The process disclosed in application Ser. No. 311,063 has come to be called the "cuprion process". In patent application Ser. No. 311,063, a continuous process for recovering copper, nickel, cobalt and molybdenum from manganese deep sea nodules is disclosed which includes the step of contacting ground manganese nodules with an ammoniacal leach solution containing cuprous ions in a reaction vessel to reduce the manganese oxides in the nodules to enable metal values such as copper, nickel, cobalt and molybdenum to be solubilized. The nodule residue is washed with an ammoniacal ammonium carbonate solution to remove these entrained metal values from the residue. The reduction liquor can be recycled to the reaction vessel in which the manganese nodules are added. To maintain a sufficient amount of cuprous ions, a reducing gas, such as carbon monoxide, is passed through the reaction vessels. In patent application Ser. No. 311,063, the reaction system disclosed is operated at temperatures between the range of 40.degree.-70.degree. C, a pH between the range of 10.6-10.8 and a pressure of approximately one atmosphere. Furthermore in that process the manganese nodules are injected into a single reaction vessel. The process described in Ser. No. 311,063 requires extremely large reactors, or large number of smaller reactors in order to process a nominal output of metal values. In addition, the process disclosed in that application is operated at a pH of about 10.6. It has been found desirable to lower the pH; however, the rate of cuprous ions regeneration is proportional to the pH, with the rate increasing as the pH increases.